In the field of fastening devices, particularly those used for fastening wood or wood-like composite materials, there is regularly a requirement for screw-in fasteners to be self-countersinking. That is, it is required that, by no more than the act of screwing the fastener into position, the fastener's structure facilitates the ability of the head of the fastener to ‘sink’ below the surface of the material such that the head finishes flush (or lower) with respect to the surface of the material.
Traditionally, a countersunk fastener head is achieved by preparing the surface of the material by removing sufficient volume of the material in a frusto-conical shape to accommodate the fastener head. This is usually done with a countersunk head attached to a drill or bore.
However, the self-countersunk fastener must be designed to obviate this preparation step. This requires that the displacement and/or compression of sufficient of the material to accommodate the volume of the fastener head must be achieved by the rotation of the fastener alone. If the head design does not perform this function effectively, a ‘mushrooming’ effect can occur where the
There are some self-countersinking fastener heads known in the prior art. U.S. Reissue Pat. No. 36,741 by Walther et al and U.S. Pat. No. 3,903,784 by the Anchor Bolt & Screw Company both disclose self-countersinking screws that feature a series of scallops arranged around a frusto-conical head that, in profile, form a series of cutting edges that engage with the wood or wood-like material to carve out a niche, while the ‘carved’ material is compressed into the scallops.
However, these designs are limited in that the combined volume of the scallops do not equal the volume of wood material required to be displaced to accommodate the entire head, leading to ‘mushrooming’ of the material, which is not desired.
Accordingly, it is an object of the present invention to provide a self-countersinking fastener that substantially alleviates the known shortcomings of the prior art.